Rim‐Based Binding of Perfluorinated Acids to Pillararenes Purifies Water

Per‐ and polyfluoroalkyl substances (PFAS) pose a rapidly increasing global problem as their widespread use and high stability lead worldwide to water contamination, with significant detrimental health effects. [1] Supramolecular chemistry has been invoked to develop materials geared towards the specific capture of PFAS from water, [2] to reduce the concentration below advisory safety limits (e.g., 70 ng/L for the sum of perfluorooctane sulfonic acid, PFOS and perfluorooctanoic acid, PFOA). Scale‐up and use in natural waters with high PFAS concentrations has hitherto posed a problem. Here we report a new type of host–guest interaction between deca‐ammonium‐functionalized pillar[5]arenes (DAF−P5s) and perfluoroalkyl acids. DAF−P5 complexes show an unprecedented 1 : 10 stoichiometry, as confirmed by isothermal calorimetry and X‐ray crystallographic studies, and high binding constants (up to 10 6 M −1 ) to various polyfluoroalkyl acids. In addition, non‐fluorinated acids do not hamper this process significantly. Immobilization of DAF−P5s allows a simple single‐time filtration of PFAS‐contaminated water to reduce the PFOS/PFOA concentration 10 6 times to 15–50 ng/L level. The effective and fast (<5 min) orthogonal binding to organic molecules without involvement of fluorinated supramolecular hosts, high breakthrough capacity (90 mg/g), and robust performance (>10 regeneration cycles without decrease in performance) set a new benchmark in PFAS‐absorbing materials.